1. Field of the Invention
The present invention relates to a controlled release fertilizer and to a method for production thereof.
2. Description of the Prior Art
Fertilizers have been used for many years to supplement nutrients in growing media.
In recent years the art has focused on techniques to deliver controlled amounts of plant nutrients to the soil or other growing media. This has been done so that, on one hand, the growing plants are not adversely deprived of nutrients and, on the other hand, an over supply of nutrients is avoided. An over supply of nutrients can result in toxicity to the plants or losses from leaching. The resulting improvement in FUE (fertilizer use efficiency) can reduce the rate and the frequency of nutrient application.
U.S. Pat. No. 5,538,531 [Hudson et al. (Hudson)] and the prior art cited therein provides a useful overview of methods of conveying controlled release properties to a particulate plant nutrient. Specifically, Hudson teaches a controlled release, particulate fertilizer product having a water soluble fertilizer central mass encased in a plurality of water insoluble, abrasion resistant coatings. At least one inner coating is a urethane reaction product derived from recited isocyanates and polyols. The outer coating is formed from an organic wax having a drop melting point in the range of from 50xc2x0 C. to 120xc2x0 C. The general teachings of Hudson and those of the Examples in Hudson make it clear that the Hudson process involves curing the urethane coating(s) around the particulate plant nutrient and, thereafter, applying to the cured urethane coating(s) the outer layer of organic wax.
It is also known in the art to pre-coat particulate plant nutrient with an organic wax or similar material as a means to regular or otherwise improve the surface of the particulate plant nutrient prior to coating thereof with the urethane forming reagents.
Despite these advances in the art, there is still room for improvement. Specifically, it would be desirable to have a controlled release fertilizer and process for production thereof which would allow for the ready customization of the release rate profile of a given particulate plant nutrient having applied thereto a given amount of urethane coating(s). It would also be desirable to be able to achieve a desirable release rate profile for a given particulate plant nutrient using significantly reduced amounts of coating materials.
It is an object of the present invention to provide a novel controlled release fertilizer which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art.
Accordingly, in one of its aspects the present invention provides a controlled release fertilizer material comprising a particulate plant nutrient surrounded by a coating which is the reaction product of a mixture comprising: a polyol, an isocyanate and an organic wax.
In another of its aspects, the present invention provides a process for producing a controlled release fertilizer material comprising the steps of:
(a) contacting a particulate plant nutrient with a mixture comprising: a polyol, an isocyanate and an organic wax to produce a coating surrounding the particulate plant nutrient; and
(b) curing the coating to produce the controlled release fertilizer material.
Thus, we have surprisingly and unexpectedly discovered that an improved controlled release fertilizer material and process for production thereofmay be achieved from a coating which is the reaction product of a mixture comprising: a polyol, an isocyanate and an organic wax. Specifically, while it is known use wax as a pre-coat before application ofthe urethane layer and/or as post-coat after application of the urethane layer, the advantages of incorporating the wax with the urethane forming reagents has heretofore been unknown. This advantages include:
(i) the ability to extend the release rate profile for a give plant nutrient having a given amount of urethane coating thereon;
(ii) the ability to achieve a desirable release rate profile using significantly less coating that used with comparable prior art coating techniques; and
(iii) the ability to obtain such a product via one-step process (i.e., compared to the multi-step processes of the prior art).
Other advantages will become apparent to those of skill in art having the present specification in hand.